1. Field of the Invention
The present invention is in the field of steam generation and more specifically relates to to a system and a method applicable to boilers, stills and like apparatus, for controlling the formation of scale therein.
2. The Prior Art
The problem of scale formation on the inside of a boiler and related pipes is encountered whenever large quantities of steam are to be produced from a supply of water that contains dissolved solids. Typically, to control the formation of scale, such boilers are operated in such a manner that for each 100 parts by weight of incoming water, 80 parts are converted to steam while the remaining 20 parts are discharged from the boiler as waste water. The concentration of dissolved solids in the discharged waste water is much greater than in the incoming water, and to a large extent, the dissolved solids are discharged with the waste water, in an effort to reduce the formation of scale within the boiler.
The 80-20 ratio is chosen to allow a margin of safety, because if the boiler should ever run dry, all of the dissolved solids would be deposited on the inside of the boiler and associated pipes, thereby clogging the pipes and reducing the transfer of heat to the liquid. From the standpoint of energy conservation, it would be desirable to discharge less than the typical 20 percent of the heated water if this could be accomplished without the risk of the boiler running dry. That is, a 90-10, or even 95-5 ratio would save an appreciable amount of energy if the risk of the boiler going dry could be avoided.
Another consideration is that the solubility of most of the typical dissolved compounds increases with increasing temperature. As water from the boiler is conducted through various pipes to the point of discharge, the water typically becomes cooler with the result that some of the dissolved compounds may be forced to come out of solution and deposit on the various pipes. This particular problem is relieved by diluting the liquid in the boiler, to avoid discharging such a highly concentrated solution. However, the concentration of dissolved matter in the boiler water is rarely measured, and in practice the problem is attacked by operating the boiler at an 80-20 ratio, for example. If the concentration of material in the incoming liquid is not very great, then the choice of an arbitrary operating ratio, such as 80-20, may be needlessly inefficient if, in fact, no problems would be encountered even if a 95-5 ratio were employed.
The present invention provides a method and system for accurately determining the concentration of dissolved matter in the boiler water, and this makes possible more efficient modes of operation.
Perhaps the most common technique employed in the prior art is for a technician to manually open a valve to collect a sample of the incoming liquid in a small container. The technician also draws a small sample of the liquid in the boiler into a different container. Thereafter, the concentration of dissolved matter in both samples is determined, and based on the results, the liquid in the boiler may be diluted.
This approach has several disadvantages. It requires the intervention of a human operator, it does not provide a continuous monitoring of the concentrations, and typically there is a moderate time lag between when the samples are taken and when the corrective action is taken. It is an object of the present invention to overcome these shortcomings of the manual method.
The present invention must be distinguished from a device known in the art as the MOGUL SOLUTROL B.RTM. which is manufactured by the Mogul Corporation of Chagrin Falls, Ohio. That device periodically samples the boiler water, and if the conductivity of the boiler water exceeds a predetermined level, the water in the boiler will be diluted under control of the device. Unlike the present invention, the Mogul device does not provide continuous sampling, and it responds only to the conductivity of the boiler water, without regard to the conductivity of the incoming water. Accordingly, it cannot be used to implement a control technique based on the ratio of the concentrations of dissolved solids. In contrast, the system of the present invention measures the conductivity of both the incoming water and the water discharged from the boiler, thereby enabling a control scheme based on the ratio of the concentrations. Also, the system of the present invention employs a continuous sampling of the concentrations.